The invention relates to speed change devices of the kind comprising a stack of discs alternating with friction rings, the discs being connected for rotation to a first shaft, inter alia a driving shaft, but free to move along the shaft, and the friction rings being disposed so that they can move along the interior of a drum but are connected for rotation with the drum, the stack being gripped between an abutment connected for translatory movement to the drum and a bell-shaped member disposed inside the drum and secured to a second shaft, inter alia a driven shaft, means being provided for clamping the stack of discs and rings, the clamping means comprising elements having complementary conjugate surfaces disposed between the bell-shaped member and the drum and adapted to exert an axial force depending on the transmitted torque, the clamping means also comprising resilient means disposed between one of the elements bearing one of the conjugate surfaces and an abutment connected for translatory movement with the drum or bell-shaped members, means being provided for moving the shafts transversely with respect to one another, thus varying the thickness of the stack and varying the speed ratio between the input and the output.
Such speed change devices are known, and described, for instance, in the French Pat. No. 1,299,609.
The invention finds particular application in the case of speed change devices for motor vehicles.
An object of the invention is to provide an improved speed change device in which the means having complementary conjugate surfaces are simple to construct but efficient and able to exert an axial force depending on the transmitted torque, irrespective of the direction thereof.